1. Field of the Invention
The present invention relates to a thermal printer and a thermal recording method. More particularly, the present invention relates to a thermal printer and a thermal printing method capable of shortening fixation time without enlarging the device size.
2. Background Arts
In a color thermal printer, a color thermosensitive recording sheet or material is used to print a full-color image thereon according to the method of the frame-sequential printing. As shown in FIG. 5, The color thermosensitive recording sheet 5 (hereinafter referred to as recording sheet) includes a support 6 and a cyan thermosensitive coloring layer 7 (cyan coloring layer), a magenta thermosensitive coloring layer 8 (magenta coloring layer) and a yellow thermosensitive coloring layer 9 (yellow coloring layer), which are formed on the support 6 in this order listed. The yellow coloring layer 7 has the highest thermal sensitivity, and the cyan coloring layer 9 has the lowest one. The color thermal printer has a thermal head to press the recording sheet 5 in print operation. The thermal head is heated according to the print data, so that respective color image is recorded to each coloring layer. At first, a yellow image is recorded onto the yellow coloring layer 7 line by line, and the yellow coloring layer 7 is fixed by applying near-ultraviolet rays. Then, a magenta image is recorded in the magenta coloring layer 8, which is fixed by applying ultraviolet rays afterward. Lastly, a cyan image is recorded to the cyan coloring layer 9 so that a full-color image is recorded to the recording sheet 5.
A fixer is used to carry out fixation of the yellow and magenta coloring layers. Two kinds of fixers are incorporated in the printer, a yellow fixer lamp and a magenta fixer lamp. As shown in FIG. 6A, each fixer 2 includes two fixer lamps 3 and a reflector 4. The fixer lamp 3 emanates ultraviolet rays of peculiar wavelength to fix corresponding coloring layer. The cyan coloring layer 9 is not fixative, because its thermal sensitivity is so low that the cyan coloring layer 9 is not colored in handling;the printed sheet 5. The reflector 4 covers the fixer lamps 3, and has an opening in its lower side, so that ultraviolet rays emanated upward is reflected toward the recording sheet 5.
As a fixation method for fixing the recording sheet by the fixer 2, a passage fixation method and a stop fixation method are used. In the passage fixation method, each coloring layer is fixed while the recording sheet 5 is fed at a certain speed below the fixer 2. FIG. 6C shows a graph of applied amount of ultraviolet rays in the passage fixation method. While the recording sheet 5 is fed from A position, corresponded to the rear end in the fixation area, to B position, corresponded to the front end in the fixation area, the coloring layer is fixed by ultraviolet rays. When the color recording sheet 5 moves A position to B position, the amount of applied rays comes up to about 280 mW. The amount is enough to fix the coloring layer.
In case of a continuous recording sheet, a shutter plate is used for covering next-recording area. When the border between the recording area (present recording area) and the next-recording area reaches the A position, the shutter plate begins moving, and follows the border at the speed equal to that at which the recording sheet 5 is conveyed. Therefore, the next-recording area is kept from being fixed by the ultraviolet rays. This fixation method has an advantage that ultraviolet rays are applied to the whole recording area uniformly, so this fixation method is applied for fixing yellow coloring layer, in which over or under fixation is mattered.
In the stop fixation method, the coloring layer is fixed by applying ultraviolet rays onto the stationary recording sheet 5 for a certain time. In practical, the length of the recording area in the advancing direction is longer than that in the fixation area, so the passage fixation method is used in the beginning of print operation. When the rear end of the recording area reaches the rear end of the fixation area, the recording sheet 5 stops. Then, ultraviolet rays are applied to the stationary recording sheet 5 until applied amount of the rear end of the recording area becomes the same as that in the front portion of the recording area. This fixation method is applied for fixing the magenta coloring layer 8, because the cyan coloring layer 9, to which cyan image is recorded afterwards, is not influenced even if excessive amount of ultraviolet rays are applied.
The stop fixation method has a disadvantage that fixation time is longer than that of the passage fixation method. This is because intensity of ultraviolet rays is different according to the position in the fixation area. As shown in FIG. 6B, there is a low-intensity area in which intensity of ultraviolet rays is lower than that in the center. To fix whole recording area completely by using the stop fixation method, it is necessary to fix the low-intensity area completely. For instance, 2.8 seconds fixation is enough to have ultraviolet rays of 280 mW, the same amount in the passage fixation method, in the C point near the center of the fixation area. On the other hand, 4.8 seconds of fixation is required to have the same amount at a position near the A position.
To solve the above problem, passage fixation method may be used for fixing the magenta coloring layer 8. In that case, if the recording sheet 5 is long, two shutter plates for yellow and magenta fixation are required. The space for an additional shutter plate increases the printer size. Moreover, printing time will be longer because the length of the passage is increased by the retracting space of the additional shutter space.
An object of the invention is to provide a thermal printer and a thermal recording method to reduce fixation time without enlarging the printer size.
To achieve the above-identified object, the thermal printer of the present invention includes a shutter plate for covering the low-intensity area in the fixation area, for changing an area to apply the electromagnetic rays into a second fixation area from a first fixation area; a shutter moving mechanism for moving the shutter plate between a first position where the electromagnetic rays are applied to the first fixation area, and a second position where the electromagnetic rays are applied to the second fixation area; and a controller for moving said shutter plate from the first position to the second position at a speed equal to conveyance of the recording material when a rear end of the recording area reaches a rear end of the first fixation area, stopping conveyance of the recording material when the rear end of the recording area reaches a rear end of the second fixation area, and stopping application of the electromagnetic rays onto a rear portion of the recording area when an amount of applied rays in the rear end of the recording area becomes is equal to that of a front portion of the recording area.
In the embodiment, the thermal printer includes a pair of feeding rollers to feed the recording sheet back and forth, and the feeding rollers area located in positions upstream of the thermal head for recording an image. The thermal printer also includes a fixer that is located in a position downstream of the thermal head. The fixer includes a fixation lamp for emanating said electromagnetic rays and a reflector for reflecting said electromagnetic rays toward said recording material.
The recording material has a yellow, magenta and cyan thermosensitive coloring layers for recording full-color image. Yellow fixation is carried out without stopping conveyance of the recording material. In magenta fixation, when the rear end of the recording area reaches to the second fixation area, the controller stops feeding the recording material, and then electromagnetic rays are applied to the stationary recording material, as described above.
In the another embodiment, the reflector includes a reflector body and a side wall that is rotatably attached to a rear side of the reflector body. The side wall is substituted for the shutter plate.
According to the present invention, since the rear end of the recording area is positioned in a high-intensity area, it is possible to shorten fixation time.